Fluorescent and colorimetric assay for determination of Cu(II) and Hg(II) using AuNPs reduced and wrapped by carbon dots

Abstract

To improve the accuracy and specificity of visual sensors for detecting Cu(II) and Hg(II), a fluorescent and colorimetric dual-modal sensor based on Au nanoparticles (AuNPs) prepared by using carbon dots (CDs) was designed. If a sensor is to be applied for the detection of targets in different environmental backgrounds, it needs to have high stability against heat, pH, and salt. To this end, CD-wrapped AuNP probes were fabricated by the in situ reaction of chloroauric acid and reductive CDs. The reductive CDs were prepared with hyperbranched polyethyleneimine (HPEI) as a carbon source. HPEI-CDs not only acted as a reducing agent but also as an excellent stabilizer in the preparation and detection application of the AuNPs. Based on multiple signal responses, including color, UV-Vis absorption, and fluorescence intensity, the HPEI-CD/AuNP nanosensor was used to realize the detection of Cu²⁺ and Hg²⁺ in the linear range 9.0×10^-10-9.0×10^-4 M and 9.0×10^-7-9.0×10^-5 M with low detection limits of 75.6 nM and 281 nM, respectively. In tap water analysis, the recovery of Cu²⁺ and Hg²⁺ by fluorescent range from 109.98-113.31% and 100.65-100.81%, and the RSD values were 0.1159-1.6317% and 3.2-5.4%, respectively. The recovery of Cu²⁺ and Hg²⁺ by colorimetric detection were 99.72-100.14% and 99.88-100.12%, and RSD values were 0.6527-0.6842% and 0.4400-0.8386%, respectively. Importantly, this sensor was applied to the accurate and sensitive detection of Cu²⁺ and Hg²⁺ in tap water and sea water. The multimode readout nanosensor exhibited strong potential for achieving simultaneous detection of two different heavy metal ions in practical applications. The novel multi-mode readout carbon dots/AuNPs sensor for Cu²⁺ and Hg²⁺ detectionshowed high sensitivity and selectivity.

Keywords: AuNPs; Carbon dots; Dual-modal; Heavy metal detection; Multiple signal responses; Visual sensors.